1. Field
The subject matter disclosed herein relates to receiving a wireless signal transmitted from a communication system such as, for example, a global navigation satellite system.
2. Information
A satellite positioning system (SPS) may comprise a system of transmitters positioned to enable entities to determine their location on the Earth based, at least in part, on signals received from the transmitters. Such a transmitter typically transmits a signal marked with a repeating pseudo-random noise (PN) code of a set number of chips and may be located on ground based control stations, user equipment and/or space vehicles. In a particular example, such transmitters may be located on Earth orbiting satellites. For example, a satellite in a constellation of a Global Navigation Satellite System (GNSS) such as Global Positioning System (GPS), Galileo, Glonass or Compass may transmit a signal marked with a PN code that is distinguishable from PN codes transmitted by other satellites in the constellation. To estimate a location at a receiver, a navigation system may determine pseudorange measurements to satellites “in view” of the receiver using well known techniques based, at least in part, on detections of PN codes in signals received from the satellites
FIG. 1 illustrates an application of an SPS system, whereby a mobile station (MS) 100 in a wireless communications system receives transmissions from space vehicles (SV) 102a, 102b, 102c, 102d in the line of sight to MS 100, and derives time measurements from four or more of the transmissions. MS 100 may provide such measurements to location server 104, which determines or estimates the position of the station from the measurements. Alternatively, the subscriber station 100 may determine or estimate its own position from this information.
Wireless communications system receivers or position location system receivers, such as, for example, mobile station 100 described above, may experience difficulties in signal acquisition and/or tracking under various conditions. Such conditions may include weak and/or fading signals, frequency drift, and noise, to name but a few examples. These conditions may result in, for example, reduced acquisition sensitivity, degraded data demodulation performance, reduced availability of signals, diminished measurement quality, and increases in “time to fix” (TTF) for a position determination.